Medical devices such as ophthalmic lenses can generally be sub-divided into two major classes, namely hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. With respect to silicone medical devices, both non-hydrogel and hydrogel silicone medical devices tend to have relatively hydrophobic, non-wettable surfaces that have a high affinity for lipids. This problem is of particular concern with contact lenses.
Those skilled in the art have long recognized the need for modifying the surface of silicone ophthalmic devices, such as contact lenses and intraocular lenses, so that they are compatible with the eye. It is known that, in general, increased hydrophilicity of a contact lens surface improves the wettability of the contact lenses. This in turn is associated with improved wear comfort of contact lenses. Additionally, the surface of the lens can affect the lens's susceptibility to deposition, particularly the deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposition can cause eye discomfort or even inflammation. In the case of extended wear lenses (i.e., lenses used without daily removal of the lens before sleep), the surface is especially important, since extended wear lens must be designed for high standards of comfort and biocompatibility over an extended period of time.
Silicone lenses have been subjected to plasma surface treatment to improve their surface properties, for example, surfaces have been rendered more hydrophilic, deposit-resistant, scratch-resistant, or otherwise modified. Examples of previously-disclosed plasma surface treatments include subjecting contact lens surfaces to a plasma comprising: an inert gas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942; and 4,214,014); various hydrocarbon monomers (see, for example, U.S. Pat. No. 4,143,949); and combinations of oxidizing agents and hydrocarbons such as water and ethanol (see, for example, WO 95/04609 and U.S. Pat. No 4,632,844). U.S. Pat. No. 4,312,575 to Peyman et al. discloses a process for providing a barrier coating on a silicone or polyurethane lens by subjecting the lens to an electrical glow discharge (plasma) process conducted by first subjecting the lens to a hydrocarbon atmosphere followed by subjecting the lens to oxygen during flow discharge, thereby increasing the hydrophilicity of the lens surface.
U.S. Pat. Nos. 4,168,112, 4,321,261 and 4,436,730, all issued to Ellis et al., disclose methods for treating a charged contact lens surface with an oppositely charged ionic polymer to form a polyelectrolyte complex on the lens surface that improves wettability.
U.S. Pat. No. 5,397,848 to Yang et al. discloses a method of incorporating hydrophilic constituents into silicone polymer materials for use in contact and intra-ocular lenses.
U.S. Pat. Nos. 5,700,559 and 5,807,636, both to Sheu et al., disclose hydrophilic articles (for example, contact lenses) comprising a substrate, an ionic polymeric layer on the substrate and a disordered polyelectrolyte coating ionically bonded to the polymeric layer.
U.S. Pat. No. 5,705,583 to Bowers et al. discloses biocompatible polymeric surface coatings. The polymeric surface coatings disclosed include coatings synthesized from monomers bearing a center of positive charge, including cationic and zwitterionic monomers.
European Patent Application EP 0 963 761 A1 discloses biomedical devices with coatings that are said to be stable, hydrophilic and antimicrobial, and which are formed using a coupling agent to bond a carboxyl-containing hydrophilic coating to the surface by ester or amide linkages.
U.S. Pat. No. 4,734,475 to Goldenberg et al. discloses a contact lens made from a hydrophobic addition polymer incorporating between about 0.5 and about 30% weight oxirane substituted units in the backbone. The oxirane substituted units are reactive with a water soluble reactive organic amine, alcohol, thiol, urea or thiourea or a sulfite, bisulfite or thiosulfite.
U.S. Pat. No. 6,428,839 to Kunzler et al. discloses a method for improving the wettability of a medical device that overcomes drawbacks of various prior approaches. This method involves (a) providing a medical device that has not been subjected to a surface oxidation treatment, and (b) contacting a surface of the medical device with a wetting agent solution that preferably includes a polymer or copolymer of (meth)acrylic acid, whereby the polymer or copolymers of meth(acrylic) acid forms a complex with the hydrophilic monomer on the contact lens surface without a surface oxidation treatment step and without the addition of a coupling agent.